Integrated circuit processor and peripheral device speeds, which for digital systems are conventionally measured by clock rate, having increased to levels where they routinely exceed the data transfer rate capabilities of the buses in the computer systems within which the devices most frequently appear. Therefore, the computer system level bus, and even more so the input/output (I/O) bus, clock capabilities bound communication between the processors and the peripherals in advanced computers. This is not unexpected in that the I/O bus typically is at the level of the printed circuit board, and as such exhibits inductance and capacitance of values materially greater than the lines within integrated circuit devices. Contention for board real estate and the input/output pins of integrated circuit devices precludes increases of the I/O bus size as a solution to the clock rate limitation.
Therefore, as generally shown in FIG. 1, what is needed is a bus interface design which in the simplest form allows a processor operating at a high clock rate to transmit and receive data at its clock rate from a peripheral operating at an analogous clock rate over a bus having a clock rate capability materially lower than the transmitting and receiving devices, namely, the processor and peripheral operating in one or the other functions. Of course, the objective must be accomplished so that the information at the processor and peripheral ends can be transmitted or received in a digital format.
The use of current sources to simultaneously transmit high frequency signals over lines bidirectionally is described in U.S. Pat. Nos. 5,578,939 and 5,568,064, the subject matter of which is incorporated herein by reference. Refinements in current source drivers and reference generators associated therewith are described in the U.S. patent applications having Ser. Nos. 08/703,318 and 08/703,317, both filed on Aug. 26, 1996. Applications and refinements of current source driven multilevel signals appear in the aforementioned U.S. patent applications having Ser. Nos. 08/770,602 and 08/770,603, both filed on Dec. 19, 1996.